In a sharply worded rebuke, the judge presiding over the criminal case against five former members of the San Diego retirement system ruled he won't step down as federal prosecutors have asked him to do.

U.S. District Judge Roger Benitez said the arguments from prosecutors that he could not be impartial were “thin” and “weak.”

Moreover, the judge said prosecutors want him off the case because he has expressed skepticism about the merits of their case against the former officials.

“The Government's motion is a pretext, and the motive is clear,” he wrote in the ruling. “Because I have raised concerns about the Government's case, it wants a fresh start with a new judge.”

The ruling issued Wednesday comes four months after a tense hearing on the recusal motion filed by prosecutors. Such a move is so rare that many longtime San Diego lawyers said they could not recall another instance in which a judge was asked to step down because of perceived impartiality.

The case has been on hold since then, but Benitez scheduled a status hearing for next week. Charged in the case are former pension system lawyer Lorraine Chapin, former fund administrator Lawrence Grissom, and former board members Cathy Lexin, Teresa Webster and Ronald Saathoff.

A grand jury indicted the five in January 2006 on charges of fraud and conspiracy in connection with the pension board's approval in 2002 of a city-sponsored plan to underfund the system while at the same time increasing retirement benefits for city workers.

Benitez has questioned the government's case and said that if the defendants did not violate any state laws, then a federal prosecution might not be able to go forward.

Lexin, Webster and Saathoff also are charged in San Diego Superior Court with violating the state conflict-of-interest law, but that case is on hold in front of the state Supreme Court. Defense lawyers contend that prosecution is flawed because there was no violation of the conflict law.

Benitez has said if that is true, there is little basis for the federal case. The government has argued that state laws do not apply at all, but told Benitez in December that one state law that could potentially support the federal case was a section of the Political Reform Act.

It was after that hearing that Assistant U.S. Attorney John Owens contended Benitez had to step down because in 1994 he admitted violating the Political Reform Act when he unsuccessfully ran for judge in Imperial County.

The violations involved late disclosure of contributions to his campaign and late disclosure of payments to sub-vendors. He said he made the mistakes because he did not understand the rules, and he paid a $3,500 fine.

Prosecutors argued Benitez would be analyzing the reform act to determine if its provisions are unconstitutional because they are too vague. That created the potential his impartiality would be questioned, Owens wrote.

Benitez ruled the constitutionality of the state law is not at issue; rather, the issue was if the federal fraud law they are charged under is too vague.

U.S. Attorney Karen Hewitt said the case would go forward after Benitez's ruling.